NanoSafe III: A User Friendly Safety Management System for Nanomaterials in Laboratories and Small Facilities

Elina Buitrago, Alke Fink, Thierry Meyer, Anna Maria Novello
2021
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Résumé

Research in nanoscience continues to bring forward a steady stream of new nanomaterials and processes that are being developed and marketed. While scientific committees and expert groups deal with the harmonization of terminology and legal challenges, risk assessors in research labs continue to have to deal with the gap between regulations and rapidly developing information. The risk assessment of nanomaterial processes is currently slow and tedious because it is performed on a material-by-material basis. Safety data sheets are rarely available for (new) nanomaterials, and even when they are, they often lack nano-specific information. Exposure estimations or measurements are difficult to perform and require sophisticated and expensive equipment and personal expertise. The use of banding-based risk assessment tools for laboratory environments is an efficient way to evaluate the occupational risks associated with nanomaterials. Herein, we present an updated version of our risk assessment tool for working with nanomaterials based on a three-step control banding approach and the precautionary principle. The first step is to determine the hazard band of the nanomaterial. A decision tree allows the assignment of the material to one of three bands based on known or expected effects on human health. In the second step, the work exposure is evaluated and the processes are classified into three “nano” levels for each specific hazard band. The work exposure is estimated using a laboratory exposure model. The result of this calculation in combination with recommended occupational exposure limits (rOEL) for nanomaterials and an additional safety factor gives the final “nano” level. Finally, we update the technical, organizational, and personal protective measures to allow nanomaterial processes to be established in research environments.

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https://infoscience.epfl.ch/record/289795?ln=fr

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Elina Buitrago, Alke Fink, Thierry Meyer, Anna Maria Novello
2021
Article

Résumé

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https://infoscience.epfl.ch/record/289795?ln=fr

À propos de ce résultat

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Publications associées (26)

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Metal-organic framework (MOFs) and related nanoporous materials have emerged as promising candidates for a variety of applications, such as gas separation and storage, catalysis, sensing, etc. Their building block structure allows us to generate a huge number of distinct materials only by changing the metal nodes and organic linkers. This, in principle, allows the design and discovery of materials that perform optimally for a given application. However, the conventional process of material development, from discovery to synthesis and performance evaluation, is too slow and expensive for exploring this enormous pool of materials. Complimentary methods are therefore needed to accelerate this process. The aim of this thesis is to investigate and expand the computational and data-driven methods for the development of nanoporous materials for gas separation and storage. The prevailing use of these methods is for high-throughput screening of the materials for a target application. However, the capability and success of such a screening approach depend on fast, reliable, and accurate prediction of material properties, as well as on the effective exploration of the chemical space. Therefore, in this thesis, we develop material descriptors for the chemistry and pore geometry of MOFs, which allow us to use machine learning to rapidly evaluate their adsorption properties with high accuracy. We next introduce a methodology to quantify the diversity of material databases to assess how well the chemical space is explored when a given material database is screened. We illustrate the importance of this diversity analysis by showing how the lack of diversity in MOF databases hinders material discovery, leads to chemical insights that are not generalisable and makes machine learning models not transferable. The promising materials discovered in a screening study are only of interest if they can be synthesised and are sufficiently stable to withstand the operating conditions of the corresponding application. Therefore, we investigate the applicability and capability of computational and data-driven methods to address some of the challenges in the material synthesis and the mechanical stability of MOFs. Material synthesis still mainly rests on the chemical intuition of synthetic chemists. Here, we introduce a method using machine learning and a genetic algorithm to capture this chemical intuition for MOF synthesis. We demonstrate how this simple approach can be powerful for guiding the synthesis of new materials. Lastly, we study how the mechanical stability of MOFs, which is fundamentally important for most of their practical applications, is affected by its underlying structure, i.e., the framework bonding topology and ligand structure. We show how this understanding can be used to develop strategies to design MOFs with enhanced mechanical stability.

EPFL2020

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At the dawn of the 21st century, mankind is facing an important energy challenge. Future energy demand can only be met by large scale exploitation of renewable energy resources. Solar energy is abundant, with a sufficient capacity for the growing energy demand. However, it is necessary to implement renewable energy storage means. Hydrogen is considered as the energy carrier of the future. An energy economy based on hydrogen is viable only if hydrogen is produced from sustainable means. Water electrolysis is the most promising technique to produce hydrogen directly from water. Yet, the efficiency is limited and electrocatalysts are required to drive both the hydrogen evolution reaction and oxygen evolution reaction. Scarce and expensive materials are currently used to drive these reactions. It is, thus, imperative that efficient Earth-abundant catalysts are developed. Nanostructuring enhances the performance of inexpensive materials for water splitting and several catalysts were studied for this goal. Chapter 2 describes the application of nanostructuring technique to the archetypical catalysts that are nickel oxides for oxygen evolution. The prepared nanoparticles show superior activity towards oxygen evolution than that of their bulk counterpart. The ultrafine size of nanoparticles synthesized allowed the exposure of a higher number of active sites. The activity for oxygen evolution was, thus, significantly enhanced. We also detailed that short conditioning of the electrode improved the performance of the evaluated materials. In chapter 3 we carefully studied nanoparticles and nanowires of nickel phosphide. The catalysts is known to be really active for hydrogen evolution. Our group suspected that this material was, also, a potential oxygen evolution catalyst. We proved, for the first time, that nickel phosphide is a remarkable oxygen evolution catalyst. Under alkaline conditions, used for oxygen evolution, we observed an in-situ formation of a core-shell heterostructure, a typical nanostructure architecture. The surface oxidation of this material allowed high oxygen evolution capabilities. We concluded that careful oxidation of nanostructured materials, as observed for nickel phosphide, is essential for the preparation of future outstanding oxygen evolution catalysts. Chapter 4 details the fabrication of direct solar-to-fuel electrode using cobalt phosphide as hydrogen evolving catalyst. Instead of using the electrical energy provided by solar energy, solar irradiation on the developed assembly allows direct hydrogen production. The careful design of the light-sensitive electrode (photocathode) is detailed. Simple incorporation of cobalt phosphide by means of photodeposition alleviates the cost of the electrode fabrication. The assembled electrode is active for hydrogen evolution under visible light irradiation. In the chapter 5 we sought to fabricate a 3-dimensional hydrogen evolving catalyst. This nanostructure is based on polymer brushes on a flat conducting substrate. Once the brushes are grown on the substrate, a molybdenum sulfide catalyst is then incorporated by simple soaking technique. We were able to tune the loading of the catalyst and the corresponding activity by changing the polymer properties. The height of the polymer was modified as well as its packing density. The resulting activity proved superior to similar approaches and to previous reports on carefully engineered molybdenum sulfide catalysts.

EPFL2017

Chargement

The world needs to think about the after fossil fuel era and while the sun baths the earth with a tremendous amount of energy, man must learn how to harvest and store it in order to dispose of a continuous supply meeting his needs. Water photo-electrolysis is a route toward the conversion of solar energy and its storage into chemical energy. Iron oxide, in the form of hematite, has been identified as a promising material, showing an excellent bandgap coupled with a high stability and abundance. However, its use is impeded by a very short charge carrier lifetime and poor oxygen evolving reaction kinetics. The former point creates the incentive for a fine nanostructuring, allowing the absorption of light close enough to the semiconductor-liquid interface for the photo-generated hole to be able to diffuse and react with water. The kinetics limitations can be overcome by mean of catalysis. In this thesis, I use a technique called atmospheric pressure chemical vapor deposition (APCVD), developed by Kay et al. in 2006 in order to fabricate hematite photoanodes that are highly nanostructured and show record solar-to-hydrogen conversion efficiencies. My work focuses on the improvement of the nanostructure in order to reduce the energy loss by deep light absorption in the material. First, the deposition parameters of the APCVD are optimized in order to improve the crystallinity of the photoanodes. The key parameter modified is the residence time of the precursor in the gas stream above the substrate. The process results in an improved overall solar energy conversion and a better electric conductivity of the material. The further application of the known best oxygen evolving catalyst – Iridium oxide – results in a record photocurrent of 3.0 mA cm−2 at 1.23 V bias vs. RHE for this class of material. In a second phase, the electrodes prepared using the newly developed conditions are analyzed by X-Ray diffraction and I find that the reduction of the residence time leads to an increased orientation of the iron oxide crystal planes. Since hematite presents a strong conduction anisotropy, and the better conducting basal planes are found perpendicular to the substrate, a correlation is made between the improved conductivity of the photoanodes prepared by reducing the residence and the preferential orientation. In order to better control the morphology of the hematite photoanodes, I present strategies of directed nucleation for the particle-assisted chemical vapor deposition. A flat model substrate is prepared as a platform for the elaboration of directing patterns. Gold nanoparticles are homogeneously deposited on the substrate with a controlled surface density. However, the chosen material reveals to be unable to initiate the iron oxide precursor decomposition and the nanoparticles show no effect on the morphology. Another patterning technique – the nanosphere lithography – is employed to create highly ordered nano-islands of a FePt alloy on the flat substrate. The dimensions of the patterning nanospheres used for the lithography controls the size and spacing of the imprints. The deposition of hematite by APCVD is successfully affected by the pattern and the size of the iron oxide nanostructures is controlled by the imprinted substrate. Finally, I combine the knowledge acquired on the directed nucleation and modified deposition conditions in order to use the APCVD in the so-called host-guest strategy. A transparent, conductive and macroporous host is built using templating TiO2 nanoparticles and a conductive niobium doped tin oxide scaffold. The host is then infiltrated by hematite using different combinations of parameters in the APCVD setup. A maximum photocurrent – equivalent to the state-of-the-art hematite host-guest strategy – is reached with a hybrid nanostructure. A dendritic formation growing atop of the macroporous host while Nb-SnO2 is conformally coated with a thin layer of hematite. By mean of parameter tuning in the APCVD system, a selective improvement of the conformal hematite layer is achieved, showing a better performance when the sample is illuminated from the substrate side as well as a modified surface morphology.

EPFL2013

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EPFL2020

EPFL2017

EPFL2013